The invention relates to a pneumatic brake device.
Such brake devices are used on rail vehicles and elsewhere, where they are often used to actuate a brake beam, which serves for pressing brake blocks against the wheel tires. Such brake devices are fitted, in particular, in the bogies of freight wagons. In order to be able to compensate for the wearing of the brake blocks and the wheel tires, an adjusting device having a spindle and an adjusting nut is usually provided. During the adjustment process a rotation of the adjusting nut is allowed, whilst the spindle remains rotationally fixed. Attachment to the brake beam is generally carried out by way of an actuator, in which the free end of the spindle terminates. Such brake devices are described in DE 103 04 715 A1 and DE 103 04 716 A1, for example.
During the normal braking process a torque acts on the spindle. This torque must not lead to any turning of the spindle, however, since this would result in an unwanted adjustment effect. The spindle, therefore, usually comprises a spindle toothed ring, which is rotationally fixed to the spindle. A yoke toothed ring is likewise rotationally fixed to the yoke of the brake device. The two toothing systems are pre-tensioned towards one another by a compression spring, so that they intermesh. During the braking process the spindle toothed ring is pressed with great force against the yoke toothed ring, so that the torque acting on the spindle can be braced and introduced into the yoke.
If the adjusting device has to be returned to its original state after changing the brake blocks, this can be achieved by deliberately turning the spindle. In so doing the two toothed rings are ratcheted against the spring force.
It has now been recognized that the toothed rings only remain in engagement if pressure is exerted on the spindle during the braking process and the spindle is moved back into its rest position after the braking process. The situation is altogether different, however, if the brake blocks have become tightly frozen to the wheels, for example, or the retaining shackles, on which the brake device is suspended, have seized up due to corrosion, for example. When moving the spindle back, a greater tensile force then occurs, which the yoke connected to the brake blocks cannot follow. As a result the toothed rings are drawn apart against the force of the compression spring. In this state the spindle may yield to the torque acting on it. The turning of the spindle results in an unintended adjustment process.
In order to prevent this, a spring-loaded pawl, which reliably prevents the toothed rings being drawn apart, may be used. This pawl is fitted to the yoke and engages in a readjustment hexagon, rotationally fixed to the spindle. If the spindle now has to be turned back into its original position by way of the readjustment hexagon after changing the brake blocks, the pawl has to be kept disengaged with one hand, leaving only the other hand free for the screwing operation. Problems of corrosion can also occur with this design, thereby preventing an easy lifting of the pawl from its locking position.